This invention is directed to paraboloid reflector antennas, and in particular to a simple feed for these antennas.
The prime focus fed paraboloid is one of the most commonly used high gain antenna systems. It has been widely used in earth-station antennas, microwave relay systems and radio-telescopes. It has a simple geometry and is generally inexpensive to fabricate. It consists of a reflecting paraboloid surface with a feed system at its focus. Since the performance of this type of antenna relates closely to its feed, the feed has to be designed for high antenna efficiency and low cross-polarization, which can be achieved with a feed having a symmetric E and H plane radiation patterns. A common feed, which has been used because of its simplicity and low cost, is a waveguide radiator supporting the dominant mode. However, this type of feed generally has asymmetric E and H plane radiation patterns, thus causing a loss in the efficiency of the reflector and a high cross-polar radiation. High efficiency feeds with symmetric E and H plane patterns are normally designed using corrugated or multi-mode horns. A common design consists of a circular waveguide with a 90.degree. corrugated flange, such as the one described in Canadian Pat. No. 873,547, which was issued to R. F. H. Yang et al on June 15, 1971, and which corresponds to U.S. Pat. No. 3,553,707, which issued on Jan. 5, 1971. It can be designed to have good symmetric patterns, to give high efficiency with reflector antennas, but due to its corrugated surface, is costly to fabricate. Recently, a feed with V-shaped corrugations has been described in a paper by C. A. Mentzer, J. R. Peters and F. B. Back, entitled "A corrugated horn antenna using V-shape corrugations", IEEE Trans., 1975, AP-23, pp. 93-97. These corrugations are somewhat easier to fabricate, however are still not satisfactory for mass production.